The present invention relates to a magnetic tape recording apparatus for recording a low frequency converted chrominance, and relates more specifically to a magnetic recording apparatus that facilitates the interleaving of a low frequency converted chrominance and an FM luminance signal by performing a frequency shift for the FM luminance signal.
Generally, a magnetic recording apparatus for the recording of video signals on magnetic tape can perform two types of recording: standard mode recording, and extended time mode recording. For a recording performed in the standard mode, the frequency of an FM luminance signal is not shifted at adjacent tracks. For a recording performed in the extended time mode, however, since the inter-track intervals are narrow and as a result increased crosstalk is generated between tracks, to prevent the image quality deterioration that thereby results, each time a track change occurs there is an fH/2 shift in the frequency of the FM luminance signal (fH denotes a horizontal scanning frequency), a process that produces a visual reduction in the deterioration of image quality due to crosstalk (this is defined as the first related art).
Another related art example is proposed in Japanese Patent Publication No. 63-308492A. According to this example of the related art, a single delay circuit is used in common by a Y/C separator, a drop out compensator, and a feedback H-correlated noise canceling circuit. Therefore, both the number of required parts and the number of the places adjustments must be made are reduced (this is defined as the second related art).
When the first related art is employed, it is accompanied by the following problem. To improve the resolution of a video signal recorded on magnetic tape, the characteristic of a high-pass filter, for removing from an FM luminance signal a signal component that overlaps a low frequency converted chrominance, is set so that on the low frequency side the value of the attenuation is also low. And when the characteristic of the high-pass filter is set so that on the low frequency side the value of attenuation is low, it is difficult to obtain a satisfactory attenuation value relative to the signal component whose frequency band overlaps the low frequency converted chrominance. As a result, the signal component of the FM luminance signal is mixed with the low frequency converted chrominance.
Further, a crystal oscillator is employed to establish a frequency of a carrier wave for a low frequency converted chrominance, and accordingly, the precision of the frequency at which the spectrum of a low frequency converted chrominance is distributed is increased. However, the frequency of the FM luminance signal fluctuates due to a shift in the value of an oscillator (a resistor or a capacitor) or a change in the level of the FM luminance signal. Therefore, an interleave relationship may be established between the spectra of the FM luminance signal and the low frequency converted chrominance, or a relationship may be established wherein these spectra overlap with each other. When the latter relationship is established, the spectrum of the FM luminance signal adversely affects the low frequency converted chrominance. And as a result, interference between the FM luminance signal and the chrominance occurs at the edge of an image, and the image quality is deteriorated.
In the second related art, the delay circuit is used in common. Therefore, even when this technique is employed, the problem encountered with the first related art is not resolved. And when the resolution of a video signal to be recorded is increased, image quality is deteriorated due to the mixing of the FM luminance signal with the low frequency converted chrominance.
It is therefore a first object of the present invention is to provide a magnetic tape recording apparatus which is able to reduce deterioration of the image quality, which is caused by the mixing of an FM luminance signal with a low frequency converted chrominance, even when the resolution of a video signal to be recorded is increased, without providing a complex structured frequency shifting unit for shifting the FM luminance signal.
In order to achieve the above object, there is provided a magnetic tape recording apparatus for recording an FM luminance signal and a low frequency converted chrominance onto tracks of a magnetic tape, wherein both of a frequency of the FM luminance signal and a spectrum distribution of the low frequency converted chrominance are shifted by fH/2 between two of the tracks corresponding to the first field and the second field of one frame of a recorded image when a horizontal scanning frequency is presumed as fH, comprising a frequency shifter for shifting the frequency of the FM luminance signal by fH/4 between two of the tracks corresponding to the second field of one frame and the first field of the subsequent frame.
The present invention may be represented as a method of recording an FM luminance signal and a low frequency converted chrominance onto tracks of a magnetic tape, comprising the steps of:
shifting both of a frequency of the FM luminance signal and a spectrum distribution of the low frequency converted chrominance by fH/2 between two of the tracks corresponding to the first field and the second field of one frame of a recorded image when a horizontal scanning frequency is presumed as fH, and
shifting the frequency of the FM luminance signal by fH/4 between two of the tracks corresponding to the second field of one frame and the first field of the subsequent frame.
Specifically, while the spectra of the low frequency converted chrominance and the FM luminance signal overlap in the frame wherein there is no fH/4 shift in the frequency of the FM luminance signal, in the frame wherein there is an fH/4 shift in the frequency of the FM luminance signal the interleaving relationship is established for these spectra. Therefore, the interleaving is established for one frame, regardless of the value of a change in the frequency of the FM luminance signal. Accordingly, even when the resolution of a video signal to be recorded is increased, deterioration of the image quality, which occurs when an FM luminance signal is mixed with a low frequency converted chrominance, is reduced.
According to the present invention, there is also provided a magnetic tape recording apparatus for recording an FM luminance signal and a low frequency converted chrominance onto tracks of a magnetic tape, wherein a spectrum distribution of the low frequency converted chrominance is shifted by fH/2 between two of the tracks corresponding to the first field and the second field of one frame of a recorded image when a horizontal scanning frequency is presumed as fH, comprising a frequency shifter for shifting the frequency of the FM luminance signal by fH/8 between two of the tracks corresponding to the second field of one frame and the first field of the subsequent frame.
The above invention may be represented as a method of recording an FM luminance signal and a low frequency converted chrominance onto tracks of a magnetic tape, comprising the steps of:
shifting a spectrum distribution of the low frequency converted chrominance by fH/2 between two of the tracks corresponding to the first field and the second field of one frame of a recorded image when a horizontal scanning frequency is presumed as fH, and
shifting a frequency of the FM luminance signal by fH/8 between two of the tracks corresponding to the second field of one frame and the first field of the subsequent frame.
Specifically, while fields wherein the spectra of the low frequency converted chrominance and the FM luminance signal overlap are generated in a frame wherein there is no fH/8 shift in the frequency of the FM luminance, in a frame wherein for these spectra there is an fH/8 shift in the frequency of the FM luminance signal, the interleaving relationship is established in the two fields. Therefore, even when the resolution of a video signal to be recorded is increased, deterioration of the image quality, which occurs when the FM luminance signal is mixed with a low frequency converted chrominance, is reduced.
Preferably, the frequency shifter includes a frequency divider for frequency half-dividing a frequency of a head switching signal for changing connection between rotary heads, and the frequency shift of the FM luminance signal is conducted by use of the frequency-divided signal of the head switching signal.
That is, the output of the frequency divider for frequency half-dividing, the frequency of the head switching signal is the output whose level is changed each time the frame is altered. Therefore, when the level of the output of the frequency divider goes to either H or L, only the frequency of the FM luminance signal need be shifted. Therefore, a frequency shifting unit that is provided for shifting the frequency of an FM luminance signal will not have a complex structure.